In general, a liquid crystal display (LCD) includes an upper substrate including a common electrode and color filters, a lower substrate including thin film transistors and pixel electrodes, and a liquid crystal material injected between the upper and lower substrates. Different electric potentials are applied to the pixel electrode and the common electrode to form an electrical field and change an arrangement of liquid crystal molecules, thereby adjusting transmissivity of light and displaying an image.
Such LCDs do not themselves produce light, and thus, they require a source of illumination in order to produce a visible image. To this end, backlight units may be used therefor. A backlight unit includes a light source for emitting light, a spread plate or light guide plate for converting a line or point light source into a surface light source, and a plurality of optical films for improving optical characteristics. Examples of an optical film used in a backlight unit include a condensing film for directing light forward to increase brightness, a spread film for hiding a defect in the rear surface of a backlight or a bright line of a light source, and a protective film for protecting an optical film from an external impact.
A condensing film, a spread film, and a protective film may be stacked. In this case, the stacked films may be closely attached to each other, thereby causing the so-called blocking, a surface defect. FIG. 1 is an image illustrating wet-out and blocking occurring when a protective film is disposed on a condensing film. In this case, an image quality of a display device may be degraded. To prevent blocking between films, protrusions spaced apart from one another by a constant distance may be arrayed on a peak of a condensing film including a lenticular lens or a prismatic lens. In this case, blocking between films can be prevented, but a lens structure and protrusions may form a moiré, thereby degrading image quality. A moiré can be prevented by irregularly arraying protrusions. However, it is technically difficult to fabricate a mold for forming protrusions irregularly arrayed on a lens structure. A condensing film including a lenticular lens or a prismatic lens may be formed using a mold having an intaglio that is formed using a bite. Thus, to fabricate a condensing film including irregularly arrayed protrusions, a frequency of processing a mold with a bite should be irregularly changed, which is difficult because the bite rotates at high speed.